Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Goes well beyond the annotations: malformed addresses are rejected with a 400 and are uncharged, failed calls are free, pricing is $0.01/call via x402 USDC or a card key with the first 25 free. The 'each call is charged, so repeats are not free' line meaningfully explains the non-obvious idempotentHint=false, which annotations alone would leave opaque.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

Front-loaded with the identity of the tool, then usage routing, then failure/pricing terms. Every sentence carries information, though the pricing sentence packs four clauses together and could be split for readability.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description still states what comes back (wei and xDAI, latest block), what input is accepted, what happens on bad input, and what the call costs. For a one-parameter read tool, nothing an agent needs is missing.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100%, so the address parameter is already documented, but the description adds a concrete example address and the validation contract (malformed input → 400, no charge). That is real added meaning, though there is only one parameter, so the upside is bounded.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb and resource — the native xDAI balance of a 0x address on Gnosis at the latest block — plus the underlying RPC (eth_getBalance) and the return units (wei and xDAI). It explicitly distinguishes itself from gnosis_token_balance and wallet_portfolio, so an agent can pick it out of a very large sibling list without opening any schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives a concrete use case ('check whether a wallet can pay gas or a transfer') and names both alternatives with the condition that selects each: gnosis_token_balance for ERC-20s and wallet_portfolio for all holdings at once. No inference required.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.